Safety paper



Patented July 4, 1933 UNITED STATES PATENT OFFICE WILLIAM N. DOUSHKESS, OF EASTON, PENNSYLVANIA, ASSIGNOR, BY MENE ASSIGN- MENTS, '10 MILTON C. JOHNSON COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SAFETY PAPER No Drawing. Original application filed larch 6, 1928, Serial No. 259,594. Divided and this application filed October 9, 1929. Serial No. 398,572.

This invention relates to safety paper and more particularly to safety paper which is adapted to prevent fraudulent changes on checks, drafts, etc. by the application of materials such as eradicators.

This application is a division of my earlier filed application, Serial No. 259,594, filed March 6, 1928, which discloses the use of leuco compounds, and particularly the leuco compounds of indamines, incorporated with or applied to paper to produce a desirable color change when bleaching or oxidizing agents are applied to the paper, which color change immediately shows any attempt that has been made to obliterate writing or other characters on the paper. The present invention has for one of its objects the preparation of a safety paper which is capable of preventing fraudulent changes of matter printed or written thereon, and is concerned with the application to or incorporation in the paper of the leuco compounds of indophenol, which similarly undergo color changes upon the application of ink eradicators and analogous materials to the paper.

In utilizing the leuco compounds of indophenol, the compound may be incorporated into the paper pulp or into the paper itself, or may be used as a coating upon the paper, or may be used for printing invisible warning indicia on the paper.

The invention is further concerned with the reduction of the sensitivity of safety papers or the materials used in making such safety papers to the action of light and air. I have found that the incorporation or additional application of metallic sulphates to the paper when a white safety paper is desired, or the inclusion of metallic sulphate in the aniline dyes if a colored safety paper is desired, will satisfactorily retard the sensitivity of the leuco compounds of the indophenols, so that while such material is not affected by light and air upon standing, it is still sensitive enough to show the desired color changes when an attempt is made to obliterate writing from such papers by the use of ink eradicators and analogous materials. Of the various metallic sulphates which satisfactorily serve for this purpose,

manganous sulphate is particularly desirable and will be considered in more detail hereinafter in connection with examples illustrating this invention. The manganous'sulphate and analogous materials partly precipitate the chemicals in the paper, particularly when an aqueous solution of the color producing compounds has been used, and this precipitation in turn tends to prevent premature oxidation. The metallic sulphates also form a non-oxidizing coating on the paper in so far as air and light affect the materials normally used in the preparation of such papers.

The substance utilized in connection with the present invention for incorporation in or coating or printing of paper in order to form satisfactory safety papers may be a product obtained by the oxidation of an amine and a member of the phenol or naphthol group to form an indophenol. The subsequent reduction of the above forms indophenol to its respective leuco compound, which would be known in the order of the above description as a leuco indophenol. This leuco compound may be then introduced into the paper pulp utilized for manufacturing the safety paper, or the leuco compound may be applied to a paper which has already been made more or less as a coating or bath therefor, or a printing thereon.

Preferably the paper is first impregnated with or mixed in the pulp stage with the indophenol leuco compound, or a water solution of the chemical is used as a bath for the paper, and then the paper is dried or partially dried and is again run thru a bath of manganous sulphate. The leuco compound and the manganous sulphate should notbe mixed. These materials, being soluble, can be utilized in aqueous solution, which is a cheaper method of use than in connection.

with insoluble compounds which may be and must be applied in other ways. The paper can be passed thru or into a bath containing the materials stated above for the purpose of saturating such materials with the compound contained in the solution, or, if desired, the paper may be passed thru a bath of the character just described for the purpose of impressing warning indicia thereon. The metallic sulphate, and particularly the man ganous sulphate set forth above, when used as a subsequent or second coating or bath for the paper serves to prevent premature oxidation of the color forming compound.

While as pointed out above, it is sometimes desirable and more economical to use materials which are soluble in water in making up the compositions which contain indophenols, such materials may be utilized in the form of insoluble salts and particularly when they are to be introduced into the paper during the pulp stage of the latter, or when they are to be formed into a colorless ink such as is used for printing invisible warning indicia on paper. The particular manner in which these materials are applied to the paper is not of great importance except in particular instances where certain preconceived results are desired. But in general, the desired compounds may be applied to the paper either by introducing the desired materials whether soluble 0r insoluble into the pulp material from which the paper is to be made, or by applying the color forming materials to the paper after the same has been formed into the the paper web, or by printing with the leuco indophenol invisible warning indicia or other design on the paper.

In using the leuco compounds, a ten per cent solution thereof has proven satisfactory. In the use of the metallic sulphate, the paper may, for example, be run thru a solution containing five pounds of metallic sulphate to twenty gallons of water.

Not only may the leuco compound be utilized as set forth above, for incorporation into the paper or as a coating therefor, but these chemicals may be used as inks for printing substantially invisible protective indicia or designs on the paper.

It is also possible within the purview of this invention to prepare the leuco compounds within the paper itself whether in sheet or pulp form. For example, the mixture of amine and phenols may be applied to or incorporated into the paper, then oxidized to the corresponding indophenol, and finally reduced back to the leuco derivative. The leuco derivative will thus be formed in sfitu within the paper whether in sheet or pulp orm.

Having thus set forth my invention, I claim:

1. A safety paper containing a leuco indophenol and a protecting metallic sulphate.

2. A safety paper carrying a leuco indophenol and manganous sulphate.

3. A safety paper made from paper pulp containing a leuco indophenol compound and subsequently treated with manganous sulphate.

4. A safety paper made from paper pulp containing a leuco indophenol material, said paper carrying a coating of manganous sulphate.

5. A safety paper carrying a coating containing indophenol producing substances and manganous sulphate.

6. In a process of making safety paper, the step of adding to the paper a leuco indophenol material and a protecting metallic sulphate.

7. In a process of making safety paper, the step of adding to the paper a composition containing an indophenol derivative and a protecting metallic sulphate.

Signed at Easton, Pennsylvania, this 25th day of September, 1929.

WILLIAM N. DOUSHKESS. 

